1994PASP..106..500G

The distribution of expansion velocities of the gas of planetary nebulae are compared to the distribution of the circumstellar envelopes of AGB stars. We have examined the relationship between ionized and neutral expansion velocities for the nebulae with detected circumnebular neutral shells. It is found that compact planetary nebulae with ionized radii less than about 0.05 pc show a distribution of expansion velocities that is similar to AGB envelopes, while large planetary nebulae with ionized radii greater than about 0.30 pc show a significantly different expansion velocity distribution than AGB envelopes. Among the large planetary nebula subset, only those nebulae of Greig's class C have an expansion velocity distribution significantly different than AGB stars, while large Grieg's class B nebulae have the same expansion velocity distribution as AGB stars. The average velocity difference between AGB stars and large Grieg's class C nebulae is well predicted by the interacting stellar winds model of planetary nebula evolution. However, the acceleration of ionized gas predicted by the interaction of stellar winds is not evident in the observed expansion velocity distribution of large Grieg's class B nebulae.